Motivation depends upon the fluctuating rhythms of fatigue

The willingness to work is not static and depends upon the fluctuating rhythms of fatigue.


Motivation is one of the driving forces behind human behavior. During extended behaviors, fatigue increases over time, leading to decreased performance in both cognitively and physically demanding tasks. Hence, Motivational fatigue is a significant barrier to successful behavior.

Low energy and motivation are something that we all experience daily. It makes us lose motivation and want to take a break.

Studies have suggested the mechanism the brain uses to decide whether a given task is worth the effort. However, the influence of fatigue on this process is not yet well understood.

In a new study, scientists at the University of Birmingham & the University of Oxford studied the impact of fatigue on a person’s decision to exert effort. It was found that people tend to work less and exert effort – even for a reward – if they were fatigued.

Two types of fatigue were detected in different parts of the brain: The first type of fatigue is short-term feeling. Little rest can conquer this type of fatigue. On the other hand, the second type is considered a longer-term feeling that stops people from working and doesn’t go away with short rest.

Tanja Müller, the first author of the study, based at the University of Oxford, said, “We found that people’s willingness to exert effort fluctuated moment by moment, but gradually declined as they repeated a task over time. Such changes in the motivation to work seem to be related to fatigue – and sometimes make us decide not to persist.”

Thirty-six young, healthy participants were tested for the study. Scientists tested the participants on a computer-based task, where they were asked to exert physical effort to obtain different amounts of monetary rewards. The participants completed more than 200 trials, and in each, they were asked if they would prefer to ‘work’ – which involved squeezing a grip force device – and gain the higher rewards offered, or to rest and only earn a small reward.

Using a mathematical model, scientists predicted how much fatigue a person would be feeling at any point in the experiment and the impact.

When participants were performing the task, scientists performed their MRI scans to observe the brain activity that matched the model’s predictions.

Dr. Matthew Apps, a senior author of the study, said“This work provides new ways of studying and understanding fatigue, its effects on the brain, and on why it can change some people’s motivation more than others. This helps begin to get to grips with something that affects many patients’ lives, as well as people while at work, school, and even elite athletes.”

Journal Reference:
  1. Müller, T., Klein-Flügge, M.C., Manohar, S.G. et al. Neural and computational mechanisms of momentary fatigue and persistence in effort-based choice. Nat Commun 12, 4593 (2021). DOI: 10.1038/s41467-021-24927-7
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